Certain steerable, wheeled work vehicles, such as truck cranes, are advantageously equipped with a variable width track. That is, one or more of the steerable wheels are extendible and retractable relative to the vehicle body. Extension of the wheels enhances the stability of the vehicle beyond normal traveling configuration with the wheels laterally retracted. Conventional types of steering mechanisms are not readily adaptable to these variable track width vehicles.
When a typical steerable, wheeled vehicle executes a turn, the radius of travel of the inside wheel on the turn is shorter than that of the outside wheel. To achieve an optimum rolling action of the wheels and avoid tire slippage, the rolling axis of the inner wheel must be at a sharper angle with the vehicle frame than the outer wheel. According to well-known Ackermann geometry, on a vehicle with front wheel steering, optimum rolling action during a turn occurs when the axes of the front wheels intersect at a point on an extension of the rear wheel axis.
On a conventional, fixed track vehicle, optimum steering geometry is acceptably approximated by a tie rod assembly. However, tie rods are fixed length links which must be physically removed and replaced to achieve such geometry at a changed track width.